XP does not have a real Dos mode.
To access the command prompt there are two commands you can use.
cmd gets a command prompt but not fullpath
command get the full path
As I understand it, cmd.exe is a 32-bit command interpreter (console). command.com is a 16-bit command interpreter, much less capable than cmd.exe.
I don't know of any way to start a version of Windows NT (XP is NT 5.1) that does not run without loading the graphical interface, even if you see what looks like a command-prompt screen. If you hit F8 before Windows loads and select Safe Mode with Command Prompt (or something like that--I don't remember exactly), you'll get a screen that looks like a DOS screen but if you notice, you'll see that the XP desktop loaded first. So it's just like loading XP as usual and choosing Run, cmd and running it full screen.
XP, W2K, and Vista users note: there is no DOS in Windows NT. There is a command prompt, however, from which you can run many very geeky commands.